1. Field of the Invention
The present invention relates to an ink jet head of an ink jet recording apparatus that records onto a recording medium such as paper by ejecting ink droplets in response to an image signal.
2. Description of Related Art
Conventionally, an ink jet head that ejects ink droplets from a nozzle has been used in a recording apparatus such as a printer. In this ink jet head, in response to an image signal a voltage is applied to a piezoelectric body which is provided corresponding to an ink chamber. The piezoelectric body is deformed based on the application of voltage after which the ink is pressurized based on this deformation of the piezoelectric body ejecting the ink from the nozzle. In this recording apparatus, the ink droplets from the nozzle are propelled onto a medium to be recorded such as paper to form an ink image on the recording medium.
For this type of ink jet head, for example, the ink jet head shown in FIG. 1 has been proposed in Japanese Unexamined Laid-open patent Hei 6-143563. This ink jet head 70 has a construction in which an elastic membrane 73 is joined to the top of a flowpath substrate 72. In the flowpath substrate 72, concave portions 71 are formed in parallel on the surface where the elastic membrane 73 is joined. The space formed between this concave portion 71 and elastic membrane 73 is used as an ink chamber 74. On the top of this elastic membrane 73 are arranged a plurality of layered vibrators for the drive 76 and two layered vibrators for the dummy 77. Each of the vibrators for the drive 76 and the vibrators for the dummy 77 is a layered piezoelectric body which is superimposed thin piezoelectric layers and thin electrode layers alternatively. The vibrators for the drive 76 and the vibrators for the dummy 77 are attached onto a substrate 75. The vibrators for the drive 76 and the vibrators for the dummy 77 are bodies which were separated by a slit process after attaching a flat plate of one piezoelectric vibrator to the substrate 75. Then, the integrated unit comprising flowpath substrate 72, elastic membrane 73, piezoelectric vibrator layers 76, 77 and the substrate 75 are held by two rigid fixing plates 78, 79.
In an ink jet head 70 constructed this way, ink droplets are ejected from a nozzle by means of applying a voltage to the vibrator for the drive 76 which deforms the vibrator and by changing the capacity of the ink chamber 74 via the elastic membrane 73 to pressurize the ink.
Furthermore, in the above-mentioned ink jet head 70, there is solid attachment of the entire surface between each of the vibrators for the drive 76 and the substrate 75 which extend in the depth direction (i.e., a direction orthogonal to the paper plane in FIG. 1). Therefore, the vibrations of the separated vibrators 76 propagate to the adjacent vibrators 76 through the substrate 75 also causing a coupled displacement to occur. Because of this, there is a possibility that problems will occur in which there is an unnecessary discharge of ink droplets from the ink chamber 74 as well as irregularity in the ink flow inside the ink chamber 74 even though the ink does not discharge resulting in undesired diameter of the ink droplets at the subsequent discharge. In other words, a mutual interference in the ink discharge characteristics which is called "cross talk" occurs resulting in poor printing quality.
Further, as a form of another ink jet head, a Kayser system ink jet head that has a vibration plate arranged in the ink chamber that is filled up with ink is well known. This vibration plate has a bimorph construction in which two or more layers of a piezoelectric member such as PZT and a metal plate are cemented (for example U.S. Pat. No. 3,946,398). In an ink jet head using the Kayser system, a voltage is applied to the vibration plate which deforms the vibration plate and then based on this deformation, the ink is pressurized and subsequently discharged.
The vibration plate in ink jet head using the above-mentioned Kayser system is comprised by a piezoelectric member. Moreover, this piezoelectric material has a construction such that it makes direct contact with the ink. Therefore, there are problems such as ink soaking into the piezoelectric material, the effective voltage applied to the piezoelectric body dropping, and the inability to obtain sufficient discharge of ink droplets.